Assembly of filamentary display devices

ABSTRACT

A refractory wire is wound in an elongated helix around and along a mandrel of a material different from that of the wire. A length of the wound mandrel is extended across and the helix thereof is bonded to spaced-apart legs of a fixture, and the mandrel is etched from within the helix. The helix is mounted between two spaced-apart terminals by disposing one leg of the fixture adjacent to one of the terminals, bonding the helix to the terminal, severing the helix from the one fixture leg, disposing the other leg of the fixture adjacent to the other terminal, bonding the helix to the other terminal, and severing the helix from the other fixture leg.

limited States Patent [72] Inventors Norman Lee Lindburg BerkeleyHeights; Hamilton David Woodland, Martinsville, both of NJ.

[21] Appl. No. 102

[22] Filed Jan. 2, I970 [45] Patented Jan. 4, 1972 [73] Assignee RCACorporation [54] ASSEMBLY OF FILAMENTARY DISPLAY 56] References CitedUNITED STATES PATENTS 1,650,605 11/1927 Campbell 140/7 1 .6

Primary ExaminerJohn F. Campbell Assistant Examiner-Victor A. Di PalmaAttorney-Glenn l-I. Bruestle ABSTRACT: A refractory wire is wound in anelongated helix around and along a mandrel of a material different fromthat of the wire. A length of the wound mandrel is extended across andthe helix thereof is bonded to spaced-apart legs of a fixture, and themandrel is etched from within the helix. The helix is mounted betweentwo spaced-apart terminals by disposing one leg of the fixture adjacentto one of the terminals, bonding the helix to the terminal, severing thehelix from the one fixture leg, disposing the other leg of the fixtureadjacent to the other terminal, bonding the helix to the other terminal,and severing the helix from the other fixture leg.

PATENTEDJAN 41972 3,631; 593

I ASSEMBLY OF FILAMENTAIRY DISPLAY DEVICES BACKGROUND OF THE INVENTIONThis invention relates to filamentary-type display devices, andparticularly to the process of fabricating and mounting the filaments ofsuch devices.

One type of display device comprises an array of electrical resistancefilaments individually mounted between pairs of support terminals. Bypassing an electrical current through various selected ones of thefilaments, to heat the filaments to incandescence, various images, e.g.,numerals, are displayed.

Generally, it is preferred that such devices be operable at low voltagesand currents. To this end, the various filaments are made of extremelysmall diameter wire, e.g., 0.0004 inch. Also, the filaments generallycomprise coils of wire, the outer diameter of the coils being extremelysmall, e.g., 0.002 inch. A problem associated with such small and thusfragile filaments is that of handling the filaments without damagingthem. Further, an especially difficult problem is that of mounting thefilaments between the terminals in an accurate and reproducible mannerwithout excessive loss of product.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of aportion of a display device, showing a substrate, the support terminalson the substrate, and an array of filaments mounted between pairs of thesupport terminals;

FIG. 2 shows, on an enlarged scale, a workpiece used in accordance withthe instant invention;

FIG. 3 shows a further workpiece, incorporating a portion of theworkpiece shown in FIG. 2, used in accordance with the instantinvention;

FIG. 4 shows one step of the use of the workpiece shown in FIG. 3; and

FIGS. 5 and 6 show subsequent steps in the use of the workpiece shown inFIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS Filamentary display devices of thetype with which this invention has utility are known. An example of suchdevices is described in U.S. Pat. No. 3,416,020, to J. A. Carley, issuedDec. 10, 1968.

In such display devices, as shown in FIG. l, a plurality of filamentarycoils 10 are mounted between pairs of support and terminal posts 12 and14, the posts being mounted on a substrate 15. In the illustrativeembodiment, two of the posts 14 are each common to two differentfilaments 10.

Means, not shown, are provided for connecting the posts 12 and 14 toterminal leads of the device, whereby electrical voltages can be appliedbetween individual pairs of posts 12 and 14 to heat the filamentsmounted between the post pairs to incandescence. Thus, various images,e.g., the numerals 0 through 9, in the illustrative embodiment, can bedisplayed.

Each filamentary coil 10 is formed of a given length of a refractorywire, e.g., tungsten with such additives as rhenium or thorium. Whenheated to incandescence, the length of the wire increases. To helpprevent sag of the heated coils, the coils are preferably mounted undertension. According to one technique, the coils are fabricated with alength less than the distance between the posts between which the coilsare to be mounted, and the coils are stretched and tensioned in themounting operation.

In accordance with the instant invention, the individual filamentarycoils 10 are provided and mounted on the support posts as follows:

A wound mandrel assembly 16 (FIG. 2) is first formed by winding arefractory wire 18 around and along a mandrel 20 of a material differentfrom the material of the wire 18. For example, using a refractory wire18 of tungsten, the mandrel 20 may be molybdenum. Means for winding finewires around and along fine mandrels are known.

In this embodiment, the wire 18 has a diameter of 0.4 mil, and is woundat 1,400 turns to the inch. The molybdenum mandrel 20 has a diameter of1.2 mils, the coil assembly 16 having an outer diameter of 0.002 inch.

The mandrel assembly 16, from which individual coils 10 are to beprovided, as described hereinafter, is significantly stronger and morerigid than an unsupported filamentary coil 10, and is relatively easy tohandle with little likelihood of damage thereto.

A length of the mandrel assembly 16 is then extended between two legs 26and 28 (FIG. 3) of a U-shaped, flat metal frame 30, bonded to the legs26 and 28, as by welding, and cut from the remainder of the assembly 16to provide a frame assembly 32, as shown. In the bonding operation, boththe mandrel 20 and the wire 18 wound thereabout are individually bondedto the frame 30. This is necessary because the mandrel 20 willeventually be removed from within the coiled filament 18.

Using fine refractory wires for both the mandrel 20 and the refractorywire 18, these materials become embedded in the material of the frame30, generally of anonrefractory material, e.g., stainless steel, using awelding bonding process.

Two dimensions of the frame assembly 32 are specifically noted. Onedimension is the distance A between the inside edges of the frame legs26 and 28. This dimension determines the amount of stretching of thefilament coil 10 when the coil is mounted between a pair of supportposts, as described hereinafter. The other dimension is the distance Bbetween the free ends 34 of the legs 26 and 28 and the point on the legswhere the mandrel assembly 16 is bonded. This dimension determines thespacing between the filament coil 10 and the substrate 15 (FIG. I), asdescribed hereinafter.

The frame 30 can be provided, for example, by a stamping process,whereby frames 30 of good dimensional accuracy can be readily andinexpensively provided. The mandrel assembly I6, being relatively rigid,as noted, can be easily and accurately positioned on the frame 30,using, for example, a simple jig, not shown, whereby frame assemblies 32can be accurately, simply, and inexpensively fabricated.

Thereafter, the mandrel 20 of the frame assembly 32 is selectivelyetched from within the wire 18 coiled thereabout. It is for this reasonthat the wire 18 and mandrel 20 should be of different materials. Usinga tungsten wire 18 and a molybdenum mandrel 20, an etchant of sulfuricand nitric acids can be used which attacks molybdenum at a much fasterrate than it does tungsten. The assembly is removed from the etchantbefore significant etching of the tungsten occurs. The frame 30, havingfurther use, described hereinafter, is made of a material resistant tothe etchant used. In the instant embodiment, for example, the frame cancomprise stainless steel or an alloy of chromium and nickel, having thetrade name Nichrome.

In another embodiment, the mandrel can comprise a low meltingtemperature material, e.g., plastic, and the mandrel removing stepcomprises heating and melting away the mandrel. Chemical dissolution canalso be used to remove such a mandrel.

Having removed the mandrel 20, a coil 10 is left suspended between thelegs 26 and 28 of the frame 30.

The frame assembly 32, without the mandrel 20, is next utilized to mountthe filamentary coil 10 between two support posts 12 and 14. As shown inFIG. 4, this is accomplished by first disposing one leg 26 of the frameassembly 32 against the outer side of the post I2 (outer with respect tothe other post 14), with the filamentary coil 10 extending across thepost 12. Also, as shown, the free ends 34 of the frame legs 26 and 28are disposed in engagement with the surface 40 of the substrate 15.

Since the distance B (FIG. 3) between the leg free ends 34 and the pointon the legs where the coil is bonded is controlled, as described,disposing the leg ends 34 against the substrate surface 40 determinesthe spacing between the coil and the substrate.

The portion of the coil I0 extending across the post 12 is then bondedto the post, as by welding or staking, or both.

Having bonded an end portion 42 of the coil 10 to the post 12, theportion of the coil between the post 12 and the frame leg 26 is broken.Owing to the fineness of the coil wire 18, the separation of the coilfrom the frame leg 26 can be done simply by moving the frame 30 slightlyaway from the post 12.

As indicated in FIG. 4, the inside distance between the frame legs 26and 28 is preferably somewhat less than the distance between theterminal posts 12 and 14. in this embodiment, for example, the distancebetween the posts 12 and M is 275 mils, and the inside distance betweenthe frame legs 26 and 28 is 170 mils.

The frame assembly 32 is then moved to dispose (as shown in FIG. 5) theframe leg 28 against the outer side of the post 14 with the coilextending across the post 14. The movement of the frame assembly 32 t0the post 14 causes stretching and tensioning of the filamentary coil 10.

The portion of the coil 10 extending across the post 14 is then bonded,at the proper height, to the post 14, and the portion of the coil 10between the post 14 and the frame leg 28 is broken by moving the frameaway, as shown in FIG. 6. This completes the coil mounting operation.

The amount of stretching ofthe coil 10 is determined by the differencein spacings between the posts 12 and 14 and between the frame legs 26and 28. While not described herein, the fabrication of substrates 15having posts 12 and M in accurately spaced relationship is well known.

We claim:

1. In a method of mounting a filament between a pair of spaced-apartterminals, the improvement comprising:

winding a filament of one material around and along a mandrel of anothermaterial to form an elongated mandrel assembly,

disposing said mandrel assembly between and securing the filamentthereof to two spaced-apart legs of a holding means,

removing said mandrel from within said mandrel assembly to leave afilament disposed between said legs,

securing said filament between'a pair of spaced-apart terminals, andthereafter disengaging said filament from said holding means. 2. Themethod of claim 1 wherein said filament to said terminals securing stepcomprises:

disposing one of said holding means legs adjacent to one of saidterminals and bonding a portion of the filament adjacent to said one legto said one terminal, and thereafter disposing the other holding meansleg adjacent to the other of said terminals and bonding a portion ofsaid filament adjacent to said other leg to said other terminal.

3. The method of claim 2 wherein:

said step of securing said filament to said holding means includesdisposing said mandrel assembly at a predetermined distance from ends ofsaid legs, and

each of said terminal bonding steps includes the step of disposing saidleg ends in engagement with a substrate on which said terminals aremounted.

4. A method of mounting a helical filament between a pair of spacedsupport terminals, comprising:

bonding ends of said filament between spaced legs of a fixture;

bonding an end portion of said filament adjacent to one of said legs toone of said terminals;

breaking the bond between said filament and said one leg;

disposing the other leg of said fixture adjacent to the other of saidterminals;

bonding an end portion of said filament adjacent to the other of saidlegs to the other of said terminals, and breaking the bond between saidfilament and said other leg.

5. The method of claim 4 wherein said filament-fixture bonding stepincludes bonding said filament at a predetermined distance from ends ofsaid legs, and

said filament-terminal bonding steps each includes the step of disposingsaid leg ends in engagement with a substrate on which said terminals aremounted.

6. The method of claim 4 wherein the spacing between said fixture legsis less than the spacing between said terminals, and including the stepof stretching said filament in said process of disposing the other legof said fixture adjacent to the other of said terminals.

1. In a method of mounting a filament between a pair of spacedapartterminals, the improvement comprising: winding a filament of onematerial around and along a mandrel of another material to form anelongated mandrel assembly, disposing said mandrel assembly between andsecuring the filament thereof to two spaced-apart legs of a holdingmeans, removing said mandrel from within said mandrel assembly to leavea filament disposed between said legs, securing said filament between apair of spaced-apart terminals, and thereafter disengaging said filamentfrom said holding means.
 2. The method of claim 1 wherein said filamentto said terminals securing step comprises: disposing one of said holdingmeans legs adjacent to one of said terminals and bonding a portion ofthe filament adjacent to said one leg to said one terminal, andthereafter disposing the other holding means leg adjacent to the otherof said terminals and bonding a portion of said filament adjacent tosaid other leg to said other terminal.
 3. The method of claim 2 wherein:said step of securing said filament to said holding means includesdisposing said mandrel assembly at a preDetermined distance from ends ofsaid legs, and each of said terminal bonding steps includes the step ofdisposing said leg ends in engagement with a substrate on which saidterminals are mounted.
 4. A method of mounting a helical filamentbetween a pair of spaced support terminals, comprising: bonding ends ofsaid filament between spaced legs of a fixture; bonding an end portionof said filament adjacent to one of said legs to one of said terminals;breaking the bond between said filament and said one leg; disposing theother leg of said fixture adjacent to the other of said terminals;bonding an end portion of said filament adjacent to the other of saidlegs to the other of said terminals, and breaking the bond between saidfilament and said other leg.
 5. The method of claim 4 wherein saidfilament-fixture bonding step includes bonding said filament at apredetermined distance from ends of said legs, and saidfilament-terminal bonding steps each includes the step of disposing saidleg ends in engagement with a substrate on which said terminals aremounted.
 6. The method of claim 4 wherein the spacing between saidfixture legs is less than the spacing between said terminals, andincluding the step of stretching said filament in said process ofdisposing the other leg of said fixture adjacent to the other of saidterminals.